This invention relates to filter arrangements and connectors.
The invention is more particularly concerned with radio frequency interference filters for connectors.
Radio frequency interference filters are commonly included in electrial connectors in order to remove interference coupled into cables, before the interference is able to enter associated electrical equipment.
In one form, these filters employ tubular or discoidal capacitors through which respective pins of the connector extend. The capacitors have one electrode soldered to the contact pin and the other electrode soldered to an earth plate.
Such filters suffer from various disadvantages. Firstly, the capacitors are fragile and liable to damage during termination of the contact pins, when being joined with wires or cables. Furthermore, the connector is expensive and the range of capacitor values is limited, restricting filtering to relatively high frequencies.
Another form of filtered connector is described in GB No. 2137436B. In this connector, the tubular capacitors for filtering are mounted on a separate plug-in assembly which is plugged in series with the connector pins. By isolating connections away from the fragile capacitors the risk of damage is reduced. However, the limitation on capacitor values is still present and there is the disadvantage of the need to make an additional series connection in the electrical path including the connector pins.
A further form of connector is described in EP No. 0124264A. In this, thick film capacitors are deposited on the earth plate, one electrode being connected with the earthed connector shell. The other electrode of the capacitor is permanently connected to the connector pin by means of solder where the pin extends through an aperture in the earth plate. Because the connector pins are connected to the filter array using solder, this makes it difficult to replace the filter array should one of the capacitors fail. Since connectors might have forty or more contact pins each with its own capacitor, there is a significant risk of one or more capacitors failing during assembly, or during termination to cables, or in adverse environments. If the entire connector has to be replaced this is expensive.